The invention relates generally to control systems for internal combustion engines, and more particularly, concerns a powertrain controller for a throttleless engine.
Conventional internal combustion engines generally fall into two categories: spark ignited (SI) engines and compression ignition (CI) engines. In general, an SI engine""s power is controlled through a process called throttling. Throttling controls the density of air that enters an engine""s combustion chambers. The throttle system is typically comprised of one or more throttle blades which are within the intake air stream. During engine idle or a closed throttle condition, the throttle blade closes off the air inlet creating a large pressure drop and density decrease. When the throttle is wide open, the throttle blade is generally parallel to the air stream and presents a minimal air restriction to inducted airflow. Under most engine operating conditions, the throttle blade is somewhere between fully open and fully closed thus presenting a controlled restriction of the intake airflow.
Fuel in an SI engine is generally introduced into the inlet air stream to provide a combustible air fuel mixture. Fuel injectors are often located in a common plenum feeding all of the cylinders on a multi-cylinder engine. When injected at this location, the engine is said to be throttle-body injected. Injectors can alternatively be located in the intake runners feeding the individual cylinder intake ports. This type of injection is referred to as port injection. Alternatively, fuel injectors can be located directly within each cylinder. This type of injection is referred to as a direct injection engine.
Power output of an internal combustion engine can also be controlled entirely by the amount of fuel introduced into the combustion chamber just prior to ignition. In CI engines such as diesel engines, the engine typically does not have a throttle. Air entering the engine is restricted only by the intake manifold design. Fuel is injected directly into the cylinder of the CI engine just prior to ignition, and ignition is caused by the high temperature generated during the piston compression stroke.
Also, alternative fuel systems have become an ever-greater concern in the search to conserve energy. Alternative energy power plants under consideration must provide the required power necessary to operate the vehicle, and at the same time be energy efficient, reduce emissions, and be cost effective. One such alternative energy power plant under consideration is a hydrogen-fueled internal combustion engine. Natural gas has also long been a potential gaseous alternate fuel for internal combustion engines.
For throttleless engine-equipped vehicles such as a variable valve timing-equipped vehicle, it is also necessary to interpret driver demand and convert it to an appropriate engine control command to deliver the desired engine/vehicle response. Prior engine control arbitration schemes typically use throttle angle as a common control variable to control airflow and, hence, engine output. See, for example, U.S. Pat. No. 5,400,865.
Interpreting driver demand and generating an appropriate engine command, however, is complicated by the existence of other sub-systems including vehicle, engine or transmission constraints such as vehicle speed limits, engine speed limits and transmission speed or torque limits. Further, in an throttleless engine, engine output must be controlled by a mechanism other than the throttle plate. Accordingly, there is a need for an arbitration scheme which selects the most appropriate engine control parameter from the various requesters. Arbitration schemes that rely upon a common control variable such as airflow by way of a throttle position may not be suitable for some vehicle and engine systems. Accordingly, there is a need for an improved engine output controller for use in throttleless engines.
The present invention provides an engine output control method and system for a vehicle having a throttleless engine system responsive to a desired engine speed signal. An engine output control method for a vehicle having a throttleless internal combustion engine system responsive to a desired engine speed signal. The method includes generating a driver demanded engine speed value corresponding to an operator input and generating a speed control system engine speed value corresponding to a predetermined speed value to permit vehicle operation at a constant speed by a speed control system. The method arbitrates between the driver demanded engine speed value and the speed control system engine speed value to derive a first desired engine speed value. This value is limited by a vehicle speed limit value, engine speed limit value, and transmission speed limit value to generate a second desired engine speed value. The engine is then controlled as a function of the second desired engine speed value and an actual engine speed value. Control of the engine output is accomplished by way of variable valve timing, fueling rate and/or fuel flow, and spark advance. In another aspect of the invention, a traction control value and transmission limiting value are generated in the torque domain and arbitrated against the speed domain-based second desired engine speed value to control the engine output.
In another embodiment of the present invention, values are generated in the acceleration domain to control the engine output. Specifically, values are generated for a driver demanded vehicle acceleration value corresponding to an accelerator pedal position; a speed control system vehicle acceleration value corresponding to a predetermined speed value to permit vehicle operation at a constant speed by a speed control system; a vehicle speed limit acceleration value corresponding to a maximum vehicle acceleration value to achieve a predetermined vehicle speed limit; and a traction control vehicle acceleration value corresponding to a maximum vehicle acceleration value to prevent wheel slip. These values are then arbitrated to derive a first desired vehicle acceleration value. The first desired vehicle acceleration value is limited by an engine speed limit value and transmission speed limit value to generate a second desired vehicle acceleration value. The resulting value can be used to control the engine output directly or converted to a desired engine acceleration value to control the engine output. Again, engine output is controlled by way of variable valve timing, fueling rate and/or fuel flow, and spark advance.
Other advantages of the invention will become apparent upon reading the following detailed description and appended claims and upon reference to the accompanying drawings.